Regulator device and method for operating a regulator device

ABSTRACT

The invention relates to a regulator device, preferably as a component of a hydraulic circuit, in particular for regulating fluid-bearing units or units that are driven using a fluid, such as adjustable fluid pumps, which respectively co-operate with at least one actuator, which can be controlled by means of at least one governor in accordance with a predefinable guide variable (p d ), said governor detecting output variables (α,p 1 ) at least partially via a recirculation line. The fact that at least one recirculation line comprises at least one monitor (estimator), which estimates the output variables (condition x) that are at least in part unknown for the assignable governor, enables the provision of a regulator device, in which the governor comprises a linear or non-linear monitor for estimating the unknown load. Said regulator device continuously monitors the load, (load volumetric flow), independently of the regulation type, (volumetric and/or pressure regulation) and its implementation, (in analogous or discrete form), in order to regulate the operation in a dynamic, precise manner (devoid of spikes).

The invention relates to a regulator device, preferably as a component of a hydraulic circuit, and a method for operating a regulator device, in particular for regulation of fluid-conveying means or means, which can be driven by a fluid, such as adjustable fluid pumps, which each interact with an actuator which, depending on a definable guide variable, can be controlled by means of at least one regulator, which acquires at least partially the output variables of the controlled system via at least one recirculation line.

DE 41 35 277 C2 discloses a regulator device for an adjustable hydraulic pump in which the delivery volume of the hydraulic pump can be changed by an actuating device and the regulator device has at least two regulators which are actuated by the actuating device and there is at least one hydraulic switching element which automatically connects the regulator to the actuating device which makes available the control pressure which is the highest or the lowest in each instance. This regulating means in one embodiment of the known solution has a pressure-rate regulator which comprises essentially a switching valve plate which is attached to the pump unit, an adjustable diaphragm unit and a rate regulator plate which is attached independently of the pressure regulator plate to the switching valve plate in the same manner as the former. According to the known solution, a control pressure is applied to one port of the pump unit there, either a control pressure delivered by the rate regulator plate or a control pressure delivered by the pressure regulator plate. At this juncture it is decided by way of the switching valve plate whether the rate regulator plate or the pressure regulator plate delivers a corresponding control signal to the indicated port. In the known solution the two regulators, i.e., the rate regulator and the pressure regulator, work independently of one another and do not directly mutually influence one another. Properties of the rate and pressure regulators which can be referred to as standard regulators are retained in the known solution, and by using these standard regulators, which can be produced economically and in large numbers, an economical solution for the known regulating means is achieved.

In particular, the known solution enables volumetric flow-regulated operation with a pressure limiting function. This type of regulation of an adjustable pump is also known under the name “LOAD SENSING”. In this operating mode the pump is regulated to a specific volumetric flow, the load pressure conversely is defined by the “constitutive law” of the load. To prevent damage to the pump or the elements in the hydraulic circuit, the “LOAD SENSING” concept contains a so-called pressure limiting function, i.e., starting from when a certain pressure level is reached switching takes place from volumetric flow-regulated operation to pressure-controlled operation.

The problems of methods known at present for volumetric flow-regulated operation with a pressure limiting function lies in switching from volumetric flow-regulated to pressure-regulated operation. This switching should take place, for example, such that regardless of the (unknown) load the desired pressure is adjusted in a manner without overshoot. This is especially important in applications in the field of injection molding machinery and/or machine tools, since in this context the pressure, on the basis of a suddenly changing load, must often be supported without overshoot at an exactly defined level.

U.S. Pat. No. 6,468,046 B1 discloses a device and a method for pressure regulation in a hydraulic pump which use the PID regulation concepts known from the prior art. In the known solution, in one embodiment for an axial piston pump, a pivoting plate which is pivotally connected to the pump is changed in its relative angle to the pump by a control valve. This regulation allows control of the control valve solely as a function of the load pressure of the pump.

U.S. Pat. No. 6,375,433 B 1 discloses a method and a device for controlling the load pressure in a hydraulic pump. In this solution, using two control laws (first feedback linearization control law, second feedback linearization control law) a nonlinear method is applied, exact input and output linearization of the pressure volumetric flow on the load side taking place.

The main problem in the currently known methods for pressure-regulated operation lies in that due to load changes the amplification of the open circuit changes greatly; this can lead to instability of the closed regulator circuit in the existing concepts. Generally high demands are imposed on the regulation quality over the entire working range of the pump and cannot be satisfactorily accommodated with these methods.

On the basis of this prior art, the object of the invention is to further improve the known solutions such that, especially when switching from volumetric flow operation to pressure-regulated operation, regardless of the unknown load situation, the desired pressure is adjusted without overshoot. Furthermore the solution according to the invention is to be characterized by stable regulation behavior and is to enable dynamic setting methods to a high degree. This object is achieved by a regulator device with the features of claim 1 and a method with the features of claim 11.

In that, as specified in the characterizing part of claim 1, at least one recirculation line has at least one monitor (estimator) which undertakes estimation of the output variables which are at least partially unknown (state x) for the assignable regulator, a regulator device is devised in which the regulator contains a linear or optionally nonlinear monitor for estimating the unknown load which, regardless of the type of regulation—volumetric and/or pressure regulation—as well as implementation—analog or discrete—continuously monitors the load (load volumetric flow) in order in this way to undertake regulation with high dynamics and exactness (without overshoot). Accordingly, very exact setting to a constant volumetric flow of the pump and/or to a constant pressure on the load side of the regulator device can be established. The method according to the invention in this respect relates to the pertinent operation of the regulator device. Including the aforementioned variables (state x) the possibility also exists of setting to a constant performance for the fluid-conveying means, for example in the form of a fluid pump. Overall, with the invention a plurality of individual regulation versions for the fluid-conveying means, for example, also in the form of a hydraulic motor, is thus achieved.

Other advantageous embodiments of the regulator device according to the invention are the subject matter of the other dependent claims.

The regulator device according to the invention and a method for its operation will be detailed below using two embodiments as shown in the drawings.

The two figures, in the form of operating diagrams, schematically show the fundamental structure of the regulator device according to the invention, not drawn to scale.

If the solution according to the invention is to be used for so-called pressure-regulated operation, the regulator shown in the figures is made in the form of a linear or nonlinear regulator, and preferably provided with disturbance variable compensation and made with a nonlinear and linear monitor (load estimator). The state variables of a simplified model with an axial pump which can be adjusted by means of an adjusting cylinder as a fluid pump (state x) are the output variables p_(actuator), α, ω, p₁ and p_(actuator) should correspond to the pressure in the adjusting cylinder, α is the pivoting angle, ω is the angular speed of pivoting, and p₁ corresponds to the pump or load pressure at the output of the intended consumption load. p_(actuator) provided with a proportionality factor can correspond to the fluid amount q_(actuator), which, as shown coming from the actuator via a spring-loaded actuating cylinder (not shown), is relayed to the axial piston pump. Preferably an axial piston pump with an adjustable pivoting disk is used, with a load which can be regarded as a type of “fluid choke” for the fluid circuit. Axial piston pumps built in this way are disclosed for example in the Mannesmann Rexroth publication Fundamentals and Components of Fluid Engineering Hydraulics (1991). In pressure-regulated operation, as can be favorably implemented especially in a regulation arrangement as shown in FIG. 1, the advantages lie especially in better guide pressure regulation since in this regulation concept the dynamic behavior can be defined at will and independently of the respective working point.

Using the so-called “adaptive backstepping” method (M. Krstic, I. Kanellakopoulos, P. Kotovic, Nonlinear and Adaptive Control Design, John Wiley & Sons, Incorporation New York, N.Y., 1995) yields the regulation law for a load case according to the constitutive law (K₁ is constant but unknown, {circumflex over (K)}₁ corresponds to the estimated value of K₁)

q ₁ =K ₁√{square root over (p ₁ −p _(r))}

with regulator parameters k_(p) and c₂, measurement variables p₁ (load pressure) and α (pivoting angle), the desired load pressure p_(d) and the pump-specific and load-specific parameters V₁, β and K_(q). The monitor (load estimator) is

$q_{actuator} = {{- {k_{p}\left( {p_{1} - p_{d}} \right)}} + {\alpha \left( {\frac{{\hat{K}}_{1}\beta}{2\; V_{1}\sqrt{p_{1} - p_{T}}} - \frac{V_{1}c_{2}}{\beta \; K_{q}}} \right)} - {\frac{V_{1}c_{2}}{\beta \; K_{q}^{2}}{\hat{K}}_{1}\sqrt{p_{1} - p_{T}}} - {{\frac{{\hat{K}}_{1}^{2}\beta}{2V_{i}K_{q}}++}\frac{{\overset{.}{\hat{K}}}_{1}}{K_{q}}\sqrt{p_{1} - p_{T}}}}$

with the adjustable parameter Y. The structure resulting from the regulation law and the monitor is shown for example in FIG. 1. In this embodiment, not the regulating variable u, but q_(actuator) is chosen as the regulating variable for the pump, since the actuator, generally in the form of a switching valve (not shown), can be assumed to be ideally fast and thus between q_(actuator) and the other regulating variable u there is only one algebraic (nonlinear) relationship which can be integrated into the actuating law (servo compensation).

The regulator circuit as shown in FIG. 1 is characterized in that for the purposes of a vector signal the pivoting angle α of the pump and the load pressure p₁ downstream from the load are combined in one (state x) which is sent once directly to the regulator and once to the monitor/estimator. The latter then in the recirculation line effects disturbance variable compensation of the estimated load (K₁) for the regulator, which moreover acquires it on the input side as a guide variable p_(d).

In the embodiment as shown in FIG. 2, the initially described solution is modified such that the parameters combined in the sum vector signal into (state x) the pivoting angle α and load pressure p₁, in turn divided, are supplied to the regulator as an input variable in the form of a sum signal which is evaluated with a factor k1 and is composed of the load pressure and the guide variable p_(d) and the other sum quantity is formed from the pivoting angle and the estimated load (or estimated pivoting angle) of the monitor/estimator which, in turn provided with the factor k2 of the regulator together with the value according to k1, forms the overall sum signal as the regulating variable u for the actuator.

In order to be able to implement volumetric flow-regulated operation with a pressure limiting function and in the process to make the transition from volumetric flow-regulated operation to pressure regulated operation (and vice versa) as smooth and as free of overshoot as possible, the concept explained above is expanded by the concept of so-called flatness (see M. J. Fliess et al, “Flatness and Defect of Non-linear Systems, Introductory Theory and Examples”, Int. J. Control, Vol. 61, no. 6. pp 1327-1361, 1995), i.e., a specific pressure and/or pressure gradient is exceeded or not reached in order to be able to switch from volume flow-regulated operation “gently” to pressure-regulated operation. For this case “gently” means that starting from the instant of switching a trajectory for the load pressure is generated in such a manner that at the instant of switching of the absolute value of the pressure and at least the first derivative of this pressure at the switching time are identical. The instant of switching is determined here (application-specifically) depending on the pressure level and the pressure gradient; (for example the maximally allowable pressure gradient is a function of the pressure level). This method also has the advantage that the pressure can be set to a certain level without overshoot.

Under comparable outline conditions as indicated for the above described pressure-controlled operation, the expanded regulation law is

$q_{actuator} = {{- {k_{p}\left( {p_{1} - p_{d}} \right)}} + {\alpha \left( {\frac{{\hat{K}}_{1}\beta}{2\; V_{1}\sqrt{p_{1} - p_{T}}} - \frac{V_{1}c_{2}}{\beta \; K_{q}}} \right)} - {\frac{V_{1}c_{2}}{\beta \; K_{q}^{2}}{\hat{K}}_{1}\sqrt{p_{1} - p_{T}}} - {{\frac{{\hat{K}}_{1}^{2}\beta}{2V_{i}K_{q}}++}\frac{{\overset{.}{\hat{K}}}_{1}}{K_{q}}\sqrt{p_{1} - p_{T}}} + \frac{{\overset{.}{p}}_{d}V_{1}^{2}c_{2}}{\beta^{2}K_{q}^{2}} + {{\overset{¨}{p}}_{d}\frac{V_{1}}{\beta \; K_{q}}}}$

and the load estimator is defined by

${\overset{.}{\hat{K}}}_{1} = {\gamma \frac{\beta}{V_{1}}\begin{pmatrix} \begin{matrix} {\frac{\beta \; {\hat{K}}_{1}\alpha}{2\; V_{1}\sqrt{p_{1} - p_{T}}} -} \\ {{\frac{\beta}{2\; V_{i}K_{q}}{\hat{K}}_{1}^{2}} - {K_{q}\left( {p_{1} - p_{T}} \right)} -} \end{matrix} \\ \frac{{\hat{K}}_{1}{\overset{.}{p}}_{d}}{2K_{q}\sqrt{p_{1} - p_{T}}} \end{pmatrix}}$

with a pressure difference stipulation p_(d) which can always be differentiated at least twice.

The combined volumetric flow and pressure regulator can be implemented either as a cascade regulator or as a linear or nonlinear state regulator with or without disturbance variable compensation and with a monitor (estimator). The output variables of the controlled system which can be detected by means of the respective monitor form a state x and, and in addition to the already mentioned variables the state x can also be monitored on the basis of other measurement variables. The output variable of the monitor (load estimator) can correspond to the load volumetric flow and can thus be designed as a function of the adjustment path (for an adjustable axial piston pump the adjustment path corresponds essentially to the angle α of the pivoting disk).

It has been found in practical tests that even for a very large sudden pressure change the load pressure can be set to the desired setpoint, for example of 180 bar, without overshoot, so that especially in the field of injection molding machinery and/or machine tools a plurality of applications are possible. 

1. A regulator device, preferably as a component of a hydraulic circuit, in particular for regulation of fluid-conveying means or means which can be driven by a fluid, such as adjustable fluid pumps, which each interact with at least one actuator which, depending on a definable guide variable (p_(d)), can be controlled by means of at least one regulator which acquires at least partially the output variables (α, p₁) of the controlled system via at least one recirculation line, characterized in that at least one recirculation line has at least one monitor (estimator) which effects estimation of the output variables which are at least partially unknown (state x) for the assignable regulator.
 2. The regulator device as claimed in claim 1, wherein the output variables (α, p₁) of the controlled system which can be acquired by means of the respective monitor form a state x which can be supplied to the monitor as a vector signal at least partially describing the system state.
 3. The regulator device as claimed in claim 2, wherein the respective vector signal includes at least one pivoting angle (α) of the fluid pump and/or the respective pressure value (p₁) of the load following the fluid pump.
 4. The regulator device as claimed in claim 1, wherein the respective vector signal can be supplied to the monitor and also, as a whole or at least one or more components of the vector signal, is used as the input variable to the assignable regulator as the input variable.
 5. The regulator device as claimed in claim 3, wherein said regulator device is designed for pressure-regulated or volumetric flow-regulated operation.
 6. The regulator device as claimed in claim 1, wherein the estimated value ({circumflex over (K)}₁) found at the output of the monitor as the input value for the assignable regulator corresponds to the load volumetric flow which is referenced to the respective load and which can be evaluated as a function of the adjustment path for the fluid pump.
 7. The regulator device as claimed in claim 6, wherein the respective regulator undergoes disturbance variable compensation by the detectable or known load volumetric flow.
 8. The regulator device as claimed in claim 1, wherein the respective regulator is implemented as a cascade regulator or as a linear or nonlinear state regulator with or without disturbance variable compensation.
 9. The regulator device as claimed in claim 1, wherein the fluid pump is an axial piston pump with a detectable output variable which relates to its pivoting angle (α).
 10. The regulator device as claimed in claim 2, wherein at least one regulator on the input side acquires at least two sum signals, one sum signal being formed from the guide variable (p_(d)) and at least one component of the vector signal, and another sum signal being formed from the estimated value of the monitor and at least one other component of the vector signal.
 11. A method for operating a regulator device, in particular for regulation of fluid-conveying means or means which can be driven by a fluid, such as adjustable fluid pumps, which each interact with at least one actuator which, depending on a definable guide variable (p_(d)), is controlled by means of at least one regulator which acquires at least partially the output variables (α, p₁) of the controlled system via at least one recirculation line which has one monitor (estimator), characterized in that a transition takes place, preferably gently, in switching from volumetric flow-regulated and pressure-limiting operation to pressure-regulated operation, and preferably vice versa, in that at the instant of switching at least the pressure value (p₁) which is used as part of the vector signal and its first time derivative run continuously. 